Current Analytical Chemistry - Volume 1, Issue 3, 2005

Sulfated polysaccharides and their oligosaccharide components play an important biological role in physiological and pathophysiological processes. Glycosaminoglycans, such as heparin, are currently used as pharmaceutical agents to control coagulation. Moreover, there are intensive efforts in developing rapid approaches for the analysis of such bioactive carbohydrates to assess their pharmacological activity and in glycomic applications. Soft ionization methods of mass spectrometry have been applied with recent success in the analysis of sulfated carbohydrates. This review will examine the application of mass spectrometry in the compositional analysis and structural characterization of these important highly charged molecules.

Recent experiences with liquid chromatography-quadrupole ion trap-mass spectrometry (LC-QITMS), as an analytical tool for determining trace amounts of organic contaminants in food and environmental samples, are addressed in this review. A brief introduction to the fundamental theory for quadrupole ion trap devices illustrates possibilities and limitations of this technique. Special attention is paid to the impact of sample preparation and chromatography on the ionization efficiency of analytes isolated from complex food and environmental matrices. The capacity to provide useful data for quantifying organic contaminants, and the possibility of obtaining structural information for identifying target and non-target compounds, are discussed. The flexibility, high sensitivity and multi-stage tandem mass spectrometric capability of the QIT are all illustrated. Contemporary applications of this technique to study organic contaminants in food and environment are presented.

The persistence of pesticides and drugs in products destined for human consumption is of great concern, in particular because of their potential carcinogenic character. However, often the transformation products formed through degradation processes possess higher toxicity than the parent compounds. It is then of primary importance not only to achieve their abatement (through purification procedures), but also to detect and identify the formed by-products, in order to evaluate their formation kinetics, stability and toxicity. For this purpose, in the present review we will study in depth, the transformation pathways followed by molecules belonging to different classes of compounds, i.e pesticides, drugs and dyes and their derivatives in photo-assisted, environmental and biological studies, where they have been identified and characterized by means of hyphenated techniques. Particular attention will be paid to degradation simulating models, such as the photocatalytic process on titanium dioxide.

Diffusion NMR, and in particular the DOSY processing method (Diffusion Ordered SpectroscopY), is an attractive technique to characterize mixtures without first having to separate the components. As a result, DOSY can yield a vast amount of analytical information. General applications of DOSY are reviewed here although we emphasize specialist applications that provide unique data. Such applications include the analysis of kinetic products, the detection of impurities in complex mixtures and the analysis of foodstuffs. We also focus on recent applications, such as the incorporation of DOSY into drug discovery protocols and as a filter in the analysis of natural product extracts or compound libraries. Depending on the characteristics of the sample under study, a careful choice of DOSY NMR experiment and its processing strategy is required to obtain optimum results. Moreover, this review describes the strengths and weakness of the different DOSY experimental and processing methods from the perspective of its application by the analytical chemist to a larger variety of sample types.

NMR based methods to screen for high-affinity ligands have become an indispensable tool for designing rationalized drugs, as these offer a combination of good experimental design of the screening process and data interpretation methods, which together provide unprecedented information on the complex nature of protein-ligand interactions. These methods rely on measuring direct changes in the spectral parameters, that are often simpler than the complex experimental procedures used to study structure and dynamics of proteins. The goal of this review article is to provide the basic details of NMR based ligand-screening methods, with particular focus on the saturation transfer difference (STD) experiment. In addition, we provide an overview of other NMR experimental methods and a practical guide on how to go about designing and implementing them.

This paper presents a comprehensive review of how recent advances in flow injection-capillary electrophoresis (FI-CE) technology have led to enhanced separation capabilities of a wide range of analytes in such areas as biological, environmental, food, medical and pharmaceutical analysis. Significant developments in design, detection methodology and applications made in the last five years are reported. In addition, future perspectives in FI-CE are considered.

In this paper, the state-of-the-art of automated solvent extraction procedures exploiting flowing stream techniques is thoroughly presented and discussed. While flow-injection liquid-liquid extraction (FI-LLE) was originally associated with the use of a solvent extractor involving a segmentor and a phase separator, current analytical trends are focused on the design and characterisation of novel strategies for the removal of the classical instrumentation aimed at improving the efficiency of phase separation as well as the repeatability, sensitivity and accuracy of the analytical chemical assays. Salient alternatives implemented in flow systems for on-line sample processing and detection of the analytes in the phase of interest, based on the principles of on-tube detection, membrane-assisted LLE, iterative forwardbackward flow, cloud-point extraction, static-phase separation, single-drop solvent extraction, and chromatomembrane separations, amongst others, are critically compared in terms of analytical performance, instrumental set-up and potential applications. Special emphasis is given in the bulk of the text to the inherent capability of sequential injection (SI) analysis to accommodate the new concept of renewable phase extraction in open tubular reactors, so-called wetting-film extraction (WFE), which is performed in the conduits of the SI assembly without the need for any ancillary hardware, thereby minimizing the risks of sample carryover. Its fundamental background, critical experimental variables, hyphenation with flow-through detectors, and analytical figures of merit are thoroughly discussed and exemplified with selected applications in the environmental and clinical field.

In recent years, microfluidic devices have been increasingly used to separate particles such as colloids, macromolecules, cells, beads and droplets. Miniaturisation often introduces new functionalities and paradigms that are not possible at conventional macroscopic scales. In this paper, split-flow-thin fractionation techniques for particle separation are reviewed and the underlying physics of particle migration is discussed. The potential of these particle separation techniques in the design of integrated microfluidic systems is described. We then illustrate how numerical simulation can provide an increased understanding of the fluid-particle motion. The advantages of numerical simulation for rational design and operation of microfluidic devices are highlighted through two practical examples involving an ultrasonic cell washing system and a quadrupole magnetic flow sorter.

Several protein sequence and structure databases have emerged from a worldwide effort to curate the information on protein sequences and their structures. Sequences are written in different formats and certain standards have evolved. On the other hand, Protein Data Bank is the largest source of information on protein structures, and sets standards on the way structural information should be written. For handling large number of protein structures and sequences in bioinformatics, a thorough understanding of the formats and contents of these databases is required. In this review, we deal with some of the most common sequence and structure databases. Several protein structure databases have emerged, dealing with special issues and varieties of protein structures. We survey the contents and availability of different databases and review their classification and mutual linking. Certain quality and financial issues on these databases are also touched upon.

This review covers the application of atomic and mass spectrometric techniques for the determination of metals and metalloids in atmospheric aerosols. Atomic spectrometric methods based on flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ETAAS), atomic fluorescence spectrometry (AFS), total reflection X-ray fluorescence (TXRF) spectrometry and plasma based techniques such as inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma-mass spectrometry (ICPMS) are reviewed, because a considerable amount of research is presently performed in this field. The application of atomic and mass spectrometric techniques for fractionation studies based on the use of chemical sequential extractions for metal partitioning in airborne particulate matter and fly ashes are also discussed. This survey contains; 156 references and covers mainly the literature published over the last decade.